Paleontologists from the University of Wisconsin-Madison uncovered a new dinosaur species that is reshaping theories about how these ancient creatures emerged and spread across the globe more than 200 million years ago. The discovery of Ahvaytum bahndooiveche, the oldest known dinosaur from Laurasia, suggests that dinosaurs may have appeared in the northern hemisphere much earlier than previously thought.
For years, scientists believed that dinosaurs first emerged in Gondwana—the southern portion of the ancient supercontinent Pangea—before migrating north to Laurasia. However, the fossils of Ahvaytum bahndooiveche, estimated to be around 230 million years old, challenge this view. Unearthed in 2013 in present-day Wyoming, which was near the equator on Laurasia at the time, the fossils indicate that dinosaurs were present in the northern hemisphere simultaneously with their southern counterparts.
"We have, with these fossils, the oldest equatorial dinosaur in the world—it's also North America's oldest dinosaur," said Dave Lovelace, a research scientist at the University of Wisconsin Geology Museum, who co-led the work with graduate student Aaron Kufner.
Discovered in a layer of rock known as the Popo Agie Formation, the remains of Ahvaytum bahndooiveche took years to analyze. While the team does not possess a complete specimen—a common challenge with early dinosaur fossils—they found sufficient bones, particularly leg parts, to identify it as a dinosaur and likely an early relative of the sauropods.
Sauropods were herbivorous giants that included some of the largest land animals in history, like the titanosaurs. In contrast, Ahvaytum bahndooiveche lived millions of years earlier and was much smaller. "It was basically the size of a chicken but with a really long tail," Lovelace described. "We think of dinosaurs as these giant behemoths, but they didn't start out that way." The specimen stood just over one foot tall and measured about three feet from head to tail.
The timing of Ahvaytum bahndooiveche's existence coincides with or follows shortly after the Carnian pluvial episode, a period of significant climatic change from approximately 234 to 232 million years ago. This era saw a shift to much wetter conditions, transforming arid deserts into more hospitable environments and possibly spurring an early diversification of dinosaur species.
Lovelace and his colleagues conducted high-precision radioisotopic dating of the rocks where the fossils were found, confirming the dinosaur's age. They also discovered an early dinosaur-like track in slightly older rocks, indicating that dinosaurs or their close relatives were present in the region even earlier.
"We're kind of filling in some of this story, and we're showing that the ideas that we've held for so long—ideas that were supported by the fragmented evidence that we had—weren't quite right," Lovelace said. "We now have this piece of evidence that shows dinosaurs were here in the northern hemisphere much earlier than we thought."
Adding to the significance of the discovery, Ahvaytum bahndooiveche is the first dinosaur species to be named in the language of the Eastern Shoshone Tribe, whose ancestral lands include the site where the fossils were found. Eastern Shoshone tribal elders and middle school students played an integral role in the naming process.
"The continuous relationship developed between Dr. Lovelace, his team, our school district, and our community is one of the most important outcomes of the discovery and naming of Ahvaytum bahndooiveche," said Amanda LeClair-Diaz, a co-author of the study and a member of the Eastern Shoshone and Northern Arapaho Tribes. She coordinated the naming process with students and tribal elders.
"Typically, the research process in communities, especially Indigenous communities, has been one-sided, with the researchers fully benefiting from studies," LeClair-Diaz explained. "The work we have done with Dr. Lovelace breaks this cycle and creates an opportunity for reciprocity in the research process."
The article was written with the assistance of a news analysis system.